1. Field of the Invention
The present invention relates to methods and compositions to reduce the neuronal cell death associated with the pro-inflammatory pathway and vasoactivity. More specifically, the present invention relates to specific modulation of signal transduction pathways, such as the sPLA2/MAPK/cPLA2/AA/LOX/COX pathway, to reduce the pro-inflammatory response that leads to an enhanced production of eicosanoids.
2. Description of Related Art
The protein β-amyloid (A4, Aβ, Aβ1-39-42) has long been central to the neuropathology of Alzheimer's disease (Glenner and Wong, 1984). However, its role in the disease process of Alzheimer's disease and other diseases, as well as its mechanism of action, remains in dispute.
It is undisputed that β-amyloid protein is a major component of the neuritic plaques which, along with the neurofibrillary tangles, provide the neuropathological diagnostic markers for Alzheimer's disease (Mattson, 1995; Vantner et al., 1991). It is also deposited around cerebral blood vessels in Alzheimer's disease (Scholz, 1938; Mandybur, 1975; Vinters, 1987).
The sequence for -amyloid is known (Glenner et al. 1984).
Emphasis has been on Alzheimer's being a neurological disease, not a vascular disease.
It has been suggested in Alzheimer's disease pathogenesis that β-amyloid has putative neurotoxic properties. However, there has been no consistent detection of such neurotoxic effects and there are conflicting reports (Price et al. 1992).
Referring to Teller et al. (1996), deposits of insoluble fibrils of amyloid -peptide (A) in the brain is a prominent neuropathological feature of all forms of Alzheimer's Disease (AD) regardless of the genetic predisposition of the subject. In addition to the deposition of A in senile plaques and neurofibrillary tangles, vascular amyloid deposition resulting in cerebral amyloid angiopathy is a hallmark of AD and related disorders such as Down's Syndrome. The abnormal accumulation of A is due to either over expression or altered processing of amyloid precursor protein (APP), a transmembrane glycoprotein. Soluble A containing forty amino acids (A40) and to a lesser degree the peptide with forty-two amino acids (A42) forms the core of the amyloid deposits. The APP gene is highly conserved across different species and APPmRNA has been detected in all tissues, suggesting a normal physiologic role for A. The cellular origin of A deposited in the brain or cerebral blood vessels in AD or its precise role in the neurodegenerative process has not been established.
Epidemiologic studies have demonstrated that anti-inflammatory therapy may be useful in the treatment of AD since a lower than expected prevalence or delayed onset of AD is apparent in patient populations using non-steroidal anti-inflammatory drugs (McGeer and McGeer, 1999; Rogers et al., 1993; and Stewart et al., 1997). Although the initiating event leading to AD-associated neuroinflammation remains speculative, the occurrence of immune system proteins, activated microglia and astrocytes among perivascular senile plaques suggests a possible involvement of Aβ in the induction of this inflammatory process (Coria et al., 1993; Griffin et al., 1995; Itagaki et al., 1989; Lue et al., 1996).
Arachidonic acid (AA) release and production of eicosanoids are prerequisites for inflammation, and phospholipase A2s (PLA2s) are key enzymes that initiate the AA cascade, which leads to the generation of multiple eicosanoid products during both acute and chronic inflammation. PLA2 activity has been shown to be elevated in disease states with a strong inflammatory component, such as rheumatoid arthritis and septic shock (Basso et al., 1990; Morita et al., 1995). PLA2s can be subdivided into several groups based upon their structures and enzymatic characteristics (Dennis, 1997). Secretory PLA2s (sPLA2s) are low molecular mass (˜14 kDa) enzymes that require a millimolar concentration of Ca2+ to exert their enzymatic action and have little fatty acid selectivity when assayed in vitro (Tischfield, J. A., 1997). Cytosolic PLA2 (cPLA2) is an ubiquitously distributed 85-kDa enzyme, and requires a submicromolar concentration of Ca2+ for effective hydrolysis of its substrate, AA-containing glycerophospholipids (Clark et al., 1991). The N-terminal CALB domain is responsible for Ca2+-dependent translocation of cPLA2 from the cytosol to perinuclear and endoplasmic reticular membranes (Glover et al., 1995), where several eicosanoid-generating enzymes, such as the two cyclooxygenases (COX-1 and COX-2) and 5-lipoxygenase (5-LOX), are located (Morita et al., 1995). Cytosolic PLA2 has multiple phosphorylation sites, among which the mitogen-activated protein kinase-directed site (Ser505) is the most critical for its activation (Lin et al, 1993).
Abnormal phospholipid metabolism has been found in AD brains, where changes were reported in concentrations of membrane phospholipids, their precursors, and catabolites, which could be evidence for abnormal PLA2 activity in these patients (Farooqui et al., 1997; Nitsch et al., 1992). Moreover, marked increases have been reported in the levels of prostaglandins and lipid peroxides in AD brain (Iwamoto et al., 1989; Jeandel et al., 1989), both products of PLA2 activity. Elevated cPLA2 immunoreactivity (Stephenson et al., 1996) has been reported in association with amyloid deposits in the cortex of AD brain, supporting the hypothesis that there is an active inflammatory process occurring in AD. Furthermore, soluble Aβ1-42 (in the pM to nM range) in a cell-free system has been shown to activate sPLA2 (Lehtonen et al., 1996), suggesting that Aβ may exert its effects either on the substrate or directly on sPLA2.
Using intact rat aortae in a tissue bath system, it was previously reported that Aβ peptides are vasoactive, and suggested that this vasoactivity could contribute to Alzheimer's pathology by reducing cerebral blood flow (Thomas et al., 1996). It has also been shown that Aβ peptides are able to enhance the vasoconstriction induced by endothelin-1 (ET-1), a potent endogenous vasoconstrictor responsible for control of cerebral vasotonus (Crawford et al., 1998) via a mechanism independent of reactive oxygen species (Paris et al., 1998). Furthermore, it was demonstrated that intra-arterial infusion of Aβ results in reduced cerebral blood flow in vivo (Suo et al., 1998), and similar impaired cerebral blood flow has been shown in transgenic mice which endogenously overproduce Aβ peptides (Iadecola, et al., 1999).
It would therefore be useful to detail the molecular mechanisms responsible for Aβ's enhancement of ET-1-induced vasoconstriction. It would also be useful to develop a method and pharmaceutical composition for counteracting such a pathway.